Nuclear power plants typically contain three major components as shown in FIG. 1: a reactor which produces superheated water which is transported to one or more steam generators; and a power turbine, driven by the steam, which generates electrical power.
The superheated water is transported to the steam generator by a tube sheet. The tube sheet in a nuclear steam generator typically forms a pair of tube members or tube rows separated by a lane, and held together by a plurality of support plates, separated at periodic intervals. The height of each tube row may exceed thirty-two feet, and include six to eight or more support plates, each separated horizontally at three to six foot intervals. In the steam generator, the tube sheets carrying the superheated water are quenched with cool water, which generates the steam which drives the turbine. The water exits through a plurality of access ports situated at the bottom of each lane.
This procedure for generating steam presents several problems. First, the water used to quench the tube sheet is supplied directly from adjacent rivers or reservoirs. Such water often has impurities or chemicals which may pierce or corrode both the steam generator tubes and the support plates. Periodic inspections of nuclear steam generators are required for obvious safety reasons connected to their operation, and steam generator cleanliness has been a problem due to such pipe corrosion and damage. The highly corrosive environment of the steam generator is particularly problematic for many of the older nuclear reactors in service throughout the world.
Heretofore, the tubes and support plates of these steam generators were inaccessible from visual inspection. Information was gathered by complicated systems which could not adequately inspect all sections of the tubes and support plates. Because of the highly radioactive environment and the heat of the pipes, direct human inspection has typically been restricted to between three and five minutes per man per six month period. This time period does not provide an ample opportunity for the careful inspection for corrosion, holes and leaks. It is particularly difficult to inspect within the narrow lanes and the tubes at the support plates, because of the heat, radioactivity and narrowness of the lanes separating the tube sheet members and the small access ports.
There are a number of issued patents directed to mechanical steam generator inspection and repair devices. U.S. Pat. No. 4,673,027 for example, discloses a device for inspecting and repairing the tubes of a nuclear reactor steam generator. The device includes a manipulator which is insertible in the chamber and which may be locked onto the tube sheet for supporting remotely controlled and monitored inspection instruments in tools. The manipulator includes a support leg which is adjustable in length in an axial direction, a main arm connected to and movable relative to the support leg and an equipment carrier which is connected to the main arm.
U.S. Pat. No. 4,653,971 discloses a device for selectively positioning a tool carried by a vehicle which moves on a perforated plate, while the device utilizes an elbow which swings a telescoping arm in the position. Similarly, U.S. Pat. No. 4,945,979 discloses an improved robotic arm for effecting a tube plugging operation. The system also includes an elbow control mechanism.
U.S. Pat. No. 4,205,939 discloses an apparatus for remotely repairing the tubes in a steam generator. The device includes a boom pivotally mounted on a column and a system for rotating the column and the boom therewith. The disclosed device further includes a tool which is operable on the tubes.
U.S. Pat. No. 4,231,419 discloses a manipulator for inspecting and repairing the tubes of heat exchangers. An inspection arm is inserted and removed through a lead-in nozzle and a swivel arm carries an extendable and retractable mouthpiece carrier with a mouthpiece which can be aligned into the tube openings. Finally, U.S. Pat. No. 4,919,194 discloses a method of positioning a robot for inspecting and maintaining operations within a nuclear plant.
While each of the above mechanism has been utilized to inspect and/or repair nuclear power steam generators and include the use of robotic manipulators or arms, none have been successfully utilized to inspect the outer diameter of the steam tube bundle or the support plates. None of the above devices can enter the 1", 2", 4", or 6" diameter apertures situated proximate to the tubes. The device disclosed in U.S. Pat. No. 4,673,027, for example, is described as entering the steam generator through a manhole, typically called the primary channel head.
There has been a long felt need for a steam generator tube sheet and support plate inspection system which can be inserted through the access ports of the steam generator, and which can be used to thoroughly inspect the tubes and support plates situated within the lanes between the tube rows. There further has been a long felt need for a support plate inspection and cleaning device which facilitates the inspection and cleaning of the rear of a steam generator and which may be insertable through the smallest access ports in the steam generator.